In recent years, the introduction of smart meters which are next-generation watt-hour meters that measure electric power digitally and are provided with a communication function within the meter, has continued to be promoted with the object of stability, efficiency, and so on, of electric power supply and demand. There is a need for a current sensor that achieves the broad dynamic range and high resolution that are required in a smart meter, with low power consumption. In order to achieve a high resolution current sensor, it is effective to employ a magnetic resistance element (MR element) having high sensitivity to a magnetic field. However, generally, in an MR element, a resistance value and magnetic field sensitivity of the element end up changing according to an incident magnetic field direction.
A DC magnetic field made incident parallel to a magnetizing moment of a magnetization fixed layer of an MR sensor acts as a DC voltage bias. A component of the DC magnetic field incident perpendicular to the magnetizing moment of the magnetization fixed layer of the MR sensor ends up changing the magnetic field sensitivity of the MR sensor. Due to such an application of bias and change of sensitivity, it may occur that a smart meter ends up displaying a mistaken current value. Moreover, there is a possibility that by applying the MR sensor with a magnetic field from the above-described direction by a magnet or the like, a display of the smart meter, and so on, may be lowered, whereby the sensor performs a mistaken display.
In the conventional technology, in order to prevent a malfunction of the above-described kind, an external magnetic field detection-dedicated magnetic field sensor is separately provided in addition to the current sensor, and a disturbance magnetic field is monitored. However, providing such an external magnetic field detection-dedicated magnetic field sensor in addition to the current sensor leads to an increase in cost of a device.